Either a 1080P or 720P sequence would work well; I tend to work in 720. The sequence settings for 1080P would be: Frame Size, 1080i (not intuitive. I know.); Pixel Aspect Ratio, Square; Field Dominance, None; for Compressor, I'd choose Pro Res 422 – nearly lossless and easy to edit.
The still image will come in as square pixels; best to keep it simple and stay with square.
Use a standard video format (e.g., 1280x720) rather than custom. The images will not totally fill the frame because they are not 16:9. Edit a matte to v1 in a color (or colors) of your choosing and put your stills on v2. Either that, or resize the images…which then may require re-framing.
The aspect ratio presets are no different than assembling your own.
QuickTime is your best choice if played from a Mac.
Because FCP needs to turn your jpegs into video clips, expect to render.
I get involved in this kind of project several times each year... what I suggest is not gospel, but it works for me.
1.) Probably the most popular viewing format these days is 1080p, which is 1920x1080 pixels. Either 24 (23.976) or 30 (29.97) fps is fine. That long list of formats you're anguishing over is for video. The odd (1440x1080, etc.) frame sizes are to accommodate various videocam recording methods; they don't apply to stills.
2.) The aspect ratio for most of the better digital cameras is NOT 16:9. And virtually all of them shoot images several times larger that 1080p. This means two things to you: A: you're going to want to pre-process your photos to crop or down-res them prior creating your sequences in order to bring the frame sizes closer to 1080, which is about as large as you can easily handle. and B: you'll want to be working with a 1080p timeline in anticipation of your final output. You will either be pillar boxing or re-framing the shots to make them "fit."
3.) Most all HD is square pixel, and progressive scan is common, so this fits nicely with your photos.
4.) Fussing with the sequence settings and altering the aspect ratios are always possiblities, but if you want an easily cut / easily playable show, stick to 1080p and save hours/days of rendering.
5.) Yes, QuickTime Movie using the timeline settings is the best quality. I always output a QT clip for a "Master" and then go to Compressor for whatever is required for delivery.
Hope this helps...
Thank you both for your helpful replies -- wish I could click "solved" on both. And I'm glad you both agree! :-)
One other quick question if you don't mind -- I have a sequence I've created that a higher frame size, 2880x1920 which is a custom 3:2 aspect ratio, and square pixels. If I export that using Quicktime Conversion and set the Size to 1280x720 (with letterboxing), will I actually lose anything? Or will I end up with the same thing as if I'd started with 1280x720? Logic tells me I'd end up with the same thing. (I don't mind pillaring.)